/*
 * Copyright 2013 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.channel;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufHolder;

/**
 * Default {@link MessageSizeEstimator} implementation which supports the
 * estimation of the size of {@link ByteBuf}, {@link ByteBufHolder} and
 * {@link FileRegion}.
 */
public final class DefaultMessageSizeEstimator implements MessageSizeEstimator
{

    private static final class HandleImpl implements Handle
    {
        private final int unknownSize;

        private HandleImpl(int unknownSize)
        {
            this.unknownSize = unknownSize;
        }

        @Override
        public int size(Object msg)
        {
            if (msg instanceof ByteBuf)
            {
                return ((ByteBuf) msg).readableBytes();
            }
            if (msg instanceof ByteBufHolder)
            {
                return ((ByteBufHolder) msg).content().readableBytes();
            }
            if (msg instanceof FileRegion)
            {
                return 0;
            }
            return unknownSize;
        }
    }

    /**
     * Return the default implementation which returns {@code 8} for unknown
     * messages.
     */
    public static final MessageSizeEstimator DEFAULT = new DefaultMessageSizeEstimator(
            8);

    private final Handle handle;

    /**
     * Create a new instance
     *
     * @param unknownSize The size which is returned for unknown messages.
     */
    public DefaultMessageSizeEstimator(int unknownSize)
    {
        if (unknownSize < 0)
        {
            throw new IllegalArgumentException(
                    "unknownSize: " + unknownSize + " (expected: >= 0)");
        }
        handle = new HandleImpl(unknownSize);
    }

    @Override
    public Handle newHandle()
    {
        return handle;
    }
}
